1. Field of the Invention
The present invention relates to an active-matrix substrate and a display device. More particularly, the present invention relates to an active-matrix substrate that can be used effectively in a liquid crystal display (LCD) as a monitor for a personal computer, a TV system or a display panel for a mobile electronic unit, for example.
2. Description of the Related Art
An LCD is a flat-panel display that has a number of advantageous features including high resolution, drastically reduced thickness and weight, and low power dissipation. The LCD market has been rapidly expanding recently as a result of tremendous improvements in its display performance, significant increases in its productivity, and a noticeable rise in its cost effectiveness over competing technologies.
The LCD has a structure in which a liquid crystal layer is sandwiched as a display medium layer between two opposed substrates. On one of the two substrates (i.e., on an active-matrix substrate), data (or source) lines, gate lines, and storage capacitor lines for use to create a storage capacitance to store a drain voltage are provided. In addition, switching elements, each of which is driven responsive to a gate signal that has been supplied through an associated one of the gate lines, and pixel electrodes, which are connected to those switching elements, are further arranged in a matrix configuration on the active-matrix substrate. A common electrode and other members are provided on the other substrate (i.e., a counter substrate). In the LCD, a predetermined voltage is applied to the liquid crystal layer through the common electrode and one of the pixel electrodes, thereby controlling the light modulating state of the liquid crystal layer. In this manner, the LCD can display an image thereon.
An active-matrix-addressed LCD that adopts a dot inversion drive technique is known as a typical active-matrix-addressed LCD. In the dot inversion drive technique, image signals to be supplied to a pair of adjacent pixels have mutually opposite polarities. An LCD of this type is disclosed in Japanese Laid-Open Publication No. 11-119193, for example. In the LCD disclosed in that publication, a common electrode, which is arranged so as to face respective pixel electrodes, is divided into multiple portions to be classified into two groups, to which signals having mutually opposite polarities are input. Also, storage capacitor lines (which will be referred to herein as “CS lines”), which are provided to create pixel storage capacitances, are also classified into two groups, to which two different signals are input as in the two groups of the common electrode. More specifically, the CS lines are classified into a group of odd-numbered CS lines and a group of even-numbered CS lines. Signals having mutually reverse phases and inverting their polarities periodically are input to these two groups.
When the CS lines are classified into two groups such that two different signals are supplied to those two groups (i.e., in driving the CS lines through two different routes), two CS trunk lines, each of which is commonly connected to an associated one of the two groups of CS lines, are typically arranged separately in the picture frame area of the active-matrix substrate (i.e., in the area outside of the display area). The predetermined signal is supplied to each group of CS lines by way of one of the two CS trunk lines.
In this case, however, the two signals to be supplied to the two groups of CS lines by way of the two CS trunk lines need to satisfy a predetermined relationship with respect to each other. To supply such signals successfully, it is important to equalize the electrical resistances of the respective CS lines that are connected to the CS trunk lines. This is because if the CS lines have significantly different electrical resistances, then even the same signal cannot be transmitted through the CS lines at the same transfer rate. That is to say, the signal being transmitted through a CS line with relatively high electrical resistance is delayed significantly from the same signal being transmitted through a CS line with a relatively low electrical resistance. In that case, the signals that are actually supplied to the respective CS lines may not satisfy the desired relationship.
Also, when two groups of CS lines are connected to two separately arranged CS trunk lines as described above, the wiring structure in the picture frame area gets relatively complicated. In that case, it is rather difficult to extend some other lines, provided between CS lines, from the area including the CS trunk line to the outer periphery of the active-matrix substrate. Such a problem can be resolved by expanding the picture frame area. However, the expansion of the picture frame area is not preferable because that is against the recent downsizing trend.
As described above, in designing an active-matrix substrate including two groups of lines to be driven by way of two different routes, the wiring structure thereof needs to be defined such that signals can be supplied appropriately to the respective groups of lines while striking an adequate balance with the other lines to be arranged.